The final draft script of "Affliction" remarked about Kelby, just after he replaces Tucker as Enterprise's chief engineer, "Although he's an experienced Starfleet officer, Kelby is still adjusting to his new position."

Kelby soon found himself overwhelmed when Klingonsabotage threatened to destroy Enterprise, necessitating Tucker's return to the ship to purge a series of subroutines which prohibited Enterprise from dropping out of warp. (ENT: "Affliction", "Divergence") When Tucker subsequently decided to stay aboard temporarily to assist in making repairs, Kelby responded negatively, feeling that his position as chief engineer was in jeopardy. (ENT: "Divergence", "Bound") At Tucker's instruction, Kelby was taken off a shuttlepod maintenance team when Tucker returned from Columbia and Kelby's place on the team was replaced by EnsignMasaro. (ENT: "Terra Prime") The tension between Kelby and Tucker came to a head when, under the influence of pheromones being produced by three Orion females who had boarded the ship, Kelby acted out his frustrations by disabling Enterprise and engaging in a fistfight with Tucker. (ENT: "Bound")

After Tucker returned full-time as Enterprise's chief engineer, Kelby remained on the engineering staff, and occasionally acted as acting-chief engineer in Tucker's absence, as he did later in 2155 when Tucker was kidnapped by xenophobicterrorist group Terra Prime aboard Orpheus Mining colony. In that capacity, Kelby oversaw efforts to ensure Enterprise could safely enter the tail of a comet headed for Mars, which allowed a shuttlepod to use the comet as camouflage to approach the planet undetected. Later, after Tucker and Commander T'Pol were rescued from Orpheus, it was briefly believed by Malcolm Reed and Travis Mayweather that Kelby was responsible for having sabotaged the shuttlepod, as his signature was on a shuttlepod maintenance log. It was soon determined that the saboteur could not have been Kelby, as Tucker had transferred Kelby off the responsible team upon his return from Columbia. Kelby's replacement, Ensign Masaro, was in fact the Terra Prime sympathizer. (ENT: "Terra Prime")

The final draft script of "Bound" established that Kelby had sexual intercourse with D'Nesh. In ultimately omitted dialogue from the same script, Kelby mentioned that Archer had told him he was doing "a great job" as Enterprise's chief engineer.

In "Bound", Kelby wears his regular commander rank insignia, but is addressed by Tucker as "lieutenant". There was no mention of him serving as a commander in the final draft of the episode's script, giving the impression he was intended to be written as a lieutenant in the episode.